A conventional hologram recorder is disclosed in Patent Document 1 for example. This hologram recorder uses so-called angular multiplex method in recording holograms. A recording beam (signal beam) is applied perpendicularly to a unit recording area in a recording medium while a reference beam (baseline beam) is applied to the unit area at a slanted angle. The reference beam is guided by two wedge-shaped prisms, a flat-plated third mirror and a parabolic mirror to the unit recording area. After passing through the wedge-shaped prisms, the reference beam is reflected by the flat-plate mirror, and then by an inner surface of the parabolic mirror before reaching the unit recording area. In this process, the wedge-shaped prisms are controlled to take appropriate attitudes so that the reference beam is directed to a desired location on the inner surface of the parabolic mirror.
Specifically, the reference beam's entering direction is varied in a rotating manner about the normal of incidence in the three-dimensional space. Further, the reference beam's entering angle is varied within a predetermined range of oblique angles with respect to the unit recording area. Each time the reference beam's entering direction and/or entering angle is varied in this way, there is an interference by the recording beam, and as a result, holograms of different interference patterns according to the different entering directions and different entering angles of the reference beam are recorded in the unit recording area of the recording medium. According to such an arrangement, it is possible to bring the reference beam into the interference from a variety of directions with respect to the recording beam, and therefore to increase hologram multiplicity in the unit recording area.
Patent Document 1: JP-A-2000-206856